Recently, a so-called head scanning ink-jet printer has been remarkably developed and used to print an image by reciprocatively scanning a printer head having a plurality of nozzles over a recording medium and selectively discharging ink from the nozzles. The head scanning ink-jet printer is widespread for commercial use as well as for consumer use.
In the head scanning ink-jet printer, a short head has hundreds of nozzles which can discharge a small amount of ink droplets. One short head is attached to a carriage for each color, and a high-quality image is formed by two-dimensional relative scanning of the carriage and the recording medium. However, the above-mentioned head scanning ink-jet printer has a problem that the printing time is longer as the image quality is higher.
FIG. 9 shows a schematic diagram showing the head scanning ink-jet printer. In the printing operation, short heads K (black), C (cyan), M (magenta), and Y (yellow) discharge ink by reciprocative scanning in the width direction of a recording medium 1. Further, the recording medium 1 is conveyed in the length direction synchronously with the scanning, so as to print the image on a printing surface of the recording medium 1 as desired.
Further, FIG. 10 shows a schematic diagram showing an ink-jet printer having long heads (full-line heads) K, C, M, and Y extended with the length corresponding to the width of a printing area of the recording medium 1. The ink-jet printer shown in FIG. 10 is a so-called full-line one-path ink-jet printer with the printable image quality that is not better than that of the above-mentioned head scanning ink-jet printer. However, the ink-jet printer shown in FIG. 10 is operated at high speed because the image is printed by conveying only the recording medium 1 only in the length direction with the long heads (full-line heads) K, C, M, and Y extended with the length corresponding to the width of the printing area of the recording medium 1.
Therefore, the ink-jet printer shown in FIG. 10 is widely used for commercial purposes which do not require the high image quality of the head scanning ink-jet printer. In this case, a continuous sheet (also referred to as roll paper or Web medium) is frequently selected as the recording medium 1 in order to effectively utilize the high speed.
In the printing operation, the long heads K, C, M, and Y having at least the width of the printing area of the recording medium 1 are aligned in the conveying direction of the recording medium 1. The image is printed by selectively discharging ink from the full-line heads K, C, M, and Y in accordance with the conveyance of the recording medium 1.
Herein, as the number of nozzles increases, it is difficult to manufacture the full-line heads K, C, M, and Y in a state for accurately holding the discharge property of the nozzles and the linearity of nozzle alignment. Therefore, as the full-line heads K, C, M, and Y are longer, the costs are increased.
According to one suggested technology, one full-line head unit is formed by continuously aligning, in the width direction of the recording medium 1, a plurality of relatively inexpensive print heads with the length which is stably manufactured.
FIG. 11 shows a schematic diagram showing an ink-jet printer using the full-line head unit. The ink-jet printer shown in FIG. 11 is a full-line one-path ink-jet printer having the alignment of the number of full-line heads corresponding to the number of using colors, and comprises a head unit UK having a plurality of heads K to cover the width of the printing area of the recording medium 1. Further, the ink-jet printer shown in FIG. 11 comprises head units UC, UM, and UY with the similar alignment, which are arranged in the conveying direction of the recording medium 1. The ink-jet printer shown in FIG. 11 prints an image on the recording medium 1 by selectively discharging ink from the head units UK, UC, UM, and UY in accordance with the conveyance of the recording medium 1.
In this case, referring to FIG. 11, individual short heads K, C, M, and Y forming the head units UK, UC, UM, and UY are diagonally aligned and, thus, the continuousness is held in the nozzle pitch in the width direction of the recording medium 1 at the junction between the short heads K (C, M, and Y).
In addition to the alignment of the plurality of short heads K (C, M, and Y) forming the one full-line head unit UK (UC, UM, and UY) shown in FIG. 11, the short heads K (C, M, and Y) are arranged in a lattice. Alternatively, the nozzles at the end portions of the same-color adjacent short heads K (C, M, and Y) are overlapped at the interval corresponding to several to dozens of nozzles in the width direction of the recording medium 1, and data printed at the overlapped portion is subjected to image processing. Thus, the conjunction between the short heads K (C, M, and Y) does not become prominent.
Meanwhile, the ink-jet printer head generally needs to properly perform the processing for recovery from the discharge capability of the nozzle during the use of the ink-jet printer head.
Typically, the discharge recovery processing is as follows.
(1) Sucking processing for removing and preventing the clog of the nozzle by sucking the ink from the nozzle
(2) Wiping processing for removing adherent ink droplets due to the smear on a nozzle surface or sucking processing and for forming the meniscus of the nozzle
(3) Spitting processing for forcedly discharging the ink to a dedicated ink tray
Some of the above-mentioned processing is not necessary, while, other processing may be necessary, depending on the ink-jet printer head. In any case, the ink-jet printer requires a function of some types of the discharge recovery processing for the printer head.
Of course, the printer head faces the position for discharging the ink droplets to the recording medium 1 during the printing operation. However, in the discharge recovery processing, the printer head needs to be moved in the direction of a discharge recovery processing unit 2 arranged to the position outside the printing area of the recording medium 1 and the printer head further needs to face the discharge recovery processing unit 2.
FIG. 12 is a schematic diagram showing a facing relationship between the recording medium 1 and the heads K, C, M, and Y in the printing operation of the ink-jet printer in a direction shown by an arrow XII shown in FIGS. 10 and 11 and showing a state in which the recording medium 1 faces the heads K, C, M, and Y.
Further, FIG. 13 is a schematic diagram showing a facing relationship between the discharge recovery processing unit 2 and the heads K, C, M, and Y in the discharge recovery processing and showing a state in which the heads K, C, M, and Y face the discharge recovery processing unit 2.
FIGS. 12 and 13 are the schematic diagrams showing the case of using the long full-line heads K, C, M, and Y shown in FIG. 10. However, the full-line heads UK, UC, UM, and UY, which are formed by combining the plurality of short heads K, C, M, and Y shown in FIG. 11, have the same principle as that of the long full-line heads K, C, M, and Y shown in FIGS. 12 and 13, and the alignments thereof and the arrangement of the corresponding discharge recovery processing unit 2 are different from those shown in FIGS. 12 and 13.
Therefore, hereinbelow, one rectangular full-line head is used for the purpose of a brief description. However, the full-line head is not limited to the single head and includes a full-line head unit comprising a plurality of short heads. Since well-known technologies can be applied to the structure and arrangement of the head and the mechanism and processing of the discharge recovery processing unit 2, the discharge recovery processing unit is a single rectangular one.
In a general facing operation of the discharge recovery processing unit 2 and the heads K, C, M, and Y in the head scanning printer, a discharge recovery mechanism is arranged out of the printing area, then, the heads K, C, M, and Y are moved to the position of the discharge recovery mechanism by using scanning mechanisms of the heads K, C, M, and Y, and the recovery processing is performed.
Further, Japanese Unexamined Patent Application Publication No. 9-57988 discloses a technology for the discharge recovery processing by moving a suction cap to a space ensured by evacuating the head in the up-direction from the printing position by a motor. This technology can be applied to a full-line printer.
Furthermore, Japanese Patent No. 2534690 discloses a method for evacuating a platen in the discharge recovery processing in an ink-jet printer using a sheet.
However, in the case of using the long head unit formed by combining one or a plurality of heads and the full-line one-path ink-jet printer using the continuous sheet, there are the following problems in the facing structure of the heads and the discharge recovery processing unit by moving the heads according to the conventional art.
(1) Misalignment of Attached Head
In many cases, the head scanning printer for consumer is formed by accurately integrating the heads corresponding to the number of used colors. Further, according to already-suggested technologies, the misalignment of the heads is suppressed by scanning the heads (by multi-paths) to the same pixel plural times.
On the other hand, in the case of the printing operation by the one path using the long head, the heads are not integrally formed and the correction processing by the multi-paths is not executed. Therefore, this requires the high accuracy (e.g., the distance between the heads and the position and rotation of nozzles in the width direction of the recording medium in the heads) for relative alignment in color heads to the recording medium.
Further, the one-path ink-jet printer is used for the commercial purpose in many cases and therefore, it is not preferable to perform registration operation frequently. The attachment accuracy needs to be kept for a long time.
The above-mentioned problems become serious, in particular, when a plurality of heads form one full-line head unit.
However, in the full-line one-path ink-jet printers, like the head scanning ink-jet printer or as disclosed in Japanese Unexamined Patent Application Publication No. 9-57988, the head portion is iteratively evacuated and returned for the discharge recovery processing and then there is a problem that the accuracy for positioning the heads is varied from the initial state thereof.
This problem necessarily causes the misalignment of registration, thus to deteriorate the printing quality.
(2) Blot on Recording Medium
In the case of using the continuous sheet, the recording medium always exists near the printing position of the head as long as the roll paper remains. Therefore, in the evacuating and returning operation of the heads for the discharge recovery processing, the positioning operation to the evacuating position and returning position causes friction or the like and the friction facilitates the fall and adhesion, on the recording medium, of ink droplets flying in all directions in the discharge recovery processing, and the recording medium might be damaged.
In order to solve the above-mentioned problem, the head portions are excessively smoothly controlled. However, in this case, the mechanism and the control operation are complicated and further cause a problem that the evacuating and returning operation requires a long time.
(3) Piping Installation of Ink Pipe
Upon using the full-line head unit comprising a plurality of heads, the piping of an ink feed pipe becomes a problem. That is, in the full-line head unit comprising a plurality of heads, the total number of heads are large. Thus, the number of ink feed pipes for feeding the ink to the heads is increased and the structure of a fluid channel of the head is complicated.
In this case, the shift of the head portion for the discharge recovery processing requires the movement of the ink feed pipe having the complicated structure of the fluid channel together with the heads. Therefore, the space for piping the ink feed pipe must be ensured and further the ink feed pipe must be set to have the optimal length. The manufacture and assembly are complicated and the manufacturing costs are increased.
(4) Avoidance of Platen on Continuous Sheet
The Japanese Patent No. 2534690 discloses the technology by which, in the printer having the recording medium as the sheet, the platen is moved in the sheet conveying direction or is opened and thus the discharge recovery processing unit faces the head portion.
However, when a driving mechanism for moving the platen is applied to the printer using the continuous sheet, the continuous sheet always exists at the position facing the head until the paper-out state of the printer. This application is impossible.
Further, the mechanism for opening the platen is applied to the one-path ink-jet printer corresponding to a plurality of colors. Then, the interval between the heads is wider depending on the evacuating space of the platen. Not only the alignment space of the heads increases but also the position of the color heads are not easily adjusted.
Furthermore, the one-path ink-jet printer has a wide area of the platen. Therefore, the interval between the sheet and the head in the printing operation does not ensure the opening operation of the platen.
Under the above-mentioned circumstances, it is an object of the present invention to provide an image forming apparatus, in which the blot on the recording medium is prevented in the discharge recovery processing of the droplet discharge means in the full-line one-path ink-jet printer, the continuous sheet as the recorded sheet is not an obstacle, the piping of the ink pipe connected to the droplet discharge means is easy, and the preferable image quality is obtained with the high positional-reproducibility of the droplet discharge means after ending the discharge recovery processing.